Diagnosis and Treatment
Acquired Atrioventricular (AV) Block in Adults
Key Points
ÎÎPatients with abnormalities of AV conduction may be asymptomatic or
may experience serious symptoms related to bradycardia, ventricular
arrhythmias, or both.
ÎÎAV block can sometimes be provoked by exercise.
ÎÎType I second-degree AV block is characterized by progressive
prolongation of the PR interval before a nonconducted beat and a
shorter PR interval after the blocked beat.
ÎÎType I second-degree AV block is usually due to delay in the AV node
irrespective of QRS width.
Because progression to advanced AV block in this situation is uncommon, pacing is
usually not indicated unless the patient is symptomatic.
ÎÎType II second-degree AV block is characterized by fixed PR intervals
before and after blocked beats and is usually associated with a wide
QRS complex.
ÎÎType II second-degree AV block is usually infranodal (either intra- or
infra-His), especially when the QRS is wide.
In these patients, symptoms are frequent, prognosis is compromised, and progression to
third-degree AV block is common and sudden. Thus, type II second-degree AV block
with a wide QRS typically indicates diffuse conduction system disease and constitutes an
indication for pacing even in the absence of symptoms.
ÎÎWhen AV conduction occurs in a 2:1 pattern, block cannot be classified
unequivocally as type I or type II, although the width of the QRS can be
suggestive.
ÎÎAdvanced second-degree AV block refers to the blocking of ≥2
consecutive P waves with some conducted beats, which indicates
some preservation of AV conduction.
In the setting of AF, a prolonged pause (eg, >5 seconds) should be considered to be due to
advanced second-degree AV block.
ÎÎThird-degree AV block (complete heart block) is defined as absence of
AV conduction.
ÎÎIn a patient with third-degree AV block, permanent pacing should
be strongly considered even when the ventricular rate is >40 bpm,
because the choice of a 40 bpm cutoff in these guidelines was not
determined from clinical trial data.
Indeed, it is not the escape rate that is necessarily critical for safety but rather the site of
origin of the escape rhythm (ie, in the AV node, the His bundle, or infra-His).
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